We intend to identify and characterize the DNA polymerase(s) which participate in the replication of simian virus 40 (SV40) DNA. Similarities between SV40 DNA replication and cellular DNA replication suggest that the same DNA polymerase(s) carry out cellular DNA replication as well. Our approach is simple: We shall purify replicating SV40 chromosomes to the maximum extent possible from infected monkey cells, then dissociate DNA polymerase(s) from the replicating chromosomes, and then use standard techniques to compare the DNA polymerase(s) so obtained with DNA polymerases alpha, beta, and gamma prepared by conventional procedures from monkey cells. Because initial purification of replicating chromosomes allows us to start with much purer material than in standard polymerase purification procedures, we feel it is worthwhile to try to purify the replication polymerase(s) to homogeneity. By partial and complete reconstitution experiments, we shall try to determine how the replication polymerase(s) interact with other proteins of the replication complex, with DNA, and with each other. If more than one polymerase species is associated with replicating SV40 chromosomes, we shall try to determine the function of each polymerase species during the replication process.